Today's mobile communication systems, such as Universal Mobile Telecommunication System (UMTS) and Global System for Mobile Communications (GSM) networks, are capable of supporting a wide variety of applications having different demands on needed transmission capability. The applications range from a simple transfer of a text message, which does not require high capacity and is not time critical, to video conferencing, which is a real time application requiring high transmission capacity. The concept of Quality of Service (QoS) was introduced to ensure that an end user, running an application, receives the system resources required for that particular application. Simultaneously, by not using more resources than necessary for the application, the use of QoS contributes to the optimization of the system resources.
In UMTS and GSM networks, bearers are defined by a QoS profile with a number of QoS attributes. Two of these QoS attributes for defining the bit rates used by the bearers, are Maximum Bit rate (MBR) and Guaranteed Bit Rate (GBR). For a bearer, both attributes, MBR and GBR may be present. Alternatively, only the MBR attribute may be present. If the GBR attribute is present, the bearer is designated as a GBR-bearer. If the GBR attribute is not present, the bearer is designated as a non-GBR bearer.
The MBR attribute is defined as the maximum number of bits delivered for that bearer at a Service Access Point (SAP) within a period of time divided by the duration of the period. The traffic conforms to the MBR as long as it follows a token bucket algorithm where the token rate equals MBR and the bucket size equals the maximum Service Data Unit (SDU) size. An example of such a token bucket algorithm is specified in 3GPP TS 23.107. The MBR is the upper limit a user or application can accept or provide. UMTS or GSM bearer service attributes may be fulfilled for traffic up to the MBR depending on the network conditions.
The GBR attribute defines the bit rate that is guaranteed or targeted within the network. The GBR is defined as the guaranteed number of bits delivered at a SAP within a period of time (provided that there is data to be delivered) divided by the duration of the period. The traffic conforms to the GBR as long as it follows a token bucket algorithm where the token rate equals GBR and the bucket size equals the maximum SDU size. The bearer QoS attributes, such as delay and reliability attributes, are guaranteed for traffic up to the GBR. For traffic exceeding the GBR, the bearer QoS attributes are not guaranteed.
The MBR attribute may be utilized to limit the delivered bit rate to applications or external networks with such limitations. In addition, the MBR attribute may be utilized to allow a maximum wanted bearer bit rate to be defined for applications able to operate with different rates, such as applications with adapting coder-decoders (codecs) utilized for example, for speech encoding.
The GBR attribute may be utilized to facilitate admission control based upon available resources and for reserving resources when setting up new bearers in the network. The GBR attribute may also be utilized for policing the bit rate for bearers in the network according to the GBR.
Existing policing schemes utilize the MBR for non-GBR bearers and the GBR for GBR bearers. The rate policing is conducted on the MBR for non-GBR bearers and rate policing is conducted upon the GBR for GBR bearers. However, existing policing schemes suffer from several disadvantages. At low loads on the network, the resources are not fully utilized for GBR bearers since the GBR bearers are not allowed to exceed their GBR for longer time periods (e.g., as defined by a token bucket algorithm) even though there is data to be sent for the bearer and available resources.